each student needs 2/5 of a cup of play dough to build a house. How many cups of play dough are needed for 9 students?

(2/5) * 9 = 18/5 = 3 3/5

To find out how many cups of play dough are needed for 9 students, we need to multiply the amount needed for each student by the number of students.

Given that each student needs 2/5 of a cup of play dough, we can set up the calculation as follows:
2/5 cup per student × 9 students.

To multiply fractions, we multiply the numerators together to get the new numerator and multiply the denominators together to get the new denominator. So, we have:
(2 × 9) / (5 × 1)
= 18 / 5

Therefore, 9 students need 18/5 cups of play dough to build their houses.